Case Study

THE SUCCESSFUL COMPLETION
of a miniature, 68-pound satellite's experimental mission earlier this
year was an important first step in the development of a technology
that promises to dramatically decrease launch costs and extend the
capabilities of uninhabited space vehicles.

The XSS-10 spacecraft -
compared in appearance to a Buick transmission - launched from Cape
Canaveral in late January 2003. It was a first-of-a-kind, low-cost
"microsatellite" carried aloft via a second-stage, modified Boeing
Delta II rocket. The 24-hour mission demonstrated autonomous operations
with newly developed guidance and control software. The expedition also
revealed some "lessons learned" that are being incorporated into a
follow-on mission called XSS-11, a one-year test of the technology.

"This launch was a small
first step toward showing the capabilities of microsatellites," Davis
says. "By operating autonomously, we eliminated a lot of the cost
associated with a larger number of people on the ground to support the
satellite."

The XSS-10 had
capabilities similar to larger satellites, but its 3-foot-long by
18-inch circumference required developers to shrink its communication
system from 12.5 to 2 pounds and reduce its power needs to one-tenth of
a previous model's requirements.

Additionally, developers
pre-programmed XSS-10's navigation and maneuvering operations into the
microsatellite's on-board computer, creating its ability to operate
autonomously. This capability contributed to the spacecraft's
relatively inexpensive launch cost of $4 million (compared to $20
million for a traditional space vehicle launch). With help from
on-board cameras, XSS-10 gathered real-time data to autonomously update
the software's algorithms once the vehicle was in orbit.

"Previously, on-orbit
maintenance of satellites was done with the inherent capabilities of
the satellite with remote guidance from a human on the ground or by
astronauts in a shuttle," explains Gen. George Harrison, director of
research operations at GTRI. "....If the microsatellite can operate
autonomously to examine and maintain itself, then you've really got
something going. It is a step toward reducing human activity in space
for routine tasks."

But microsatellite technology is still immature, Davis adds. His
research team was successful in completing the XSS-10 mission
objectives, including inspections, powering the spacecraft on and off,
and communicating with the vehicle's computer via their own
ground-based control center, rather than a central control center. But
at 1 kilometer out from the rocket, the XSS-10 was not able to
reacquire a telemetry signal from the Delta vehicle that launched it
into orbit. Researchers have already devised a fix for this problem for
future missions.

"We
are excited about the success of the XSS-10 mission," Davis says. "We
found there were a number of variables, some of which controlled us and
many of which we were able to control. We learned we had to depend on
each other, and we had some good luck. So we were successful."

Though
the scientific results of the XSS-10 mission may seem small in
comparison to those from a typical shuttle flight, they provided a
critical first step toward autonomous satellite operations, Harrison
notes.

"This
is the way science progresses," he explains. "You set real, achievable
goals and develop the science and technology to achieve them. Then you
prove them through flight or orbital tests.... So then the next mission
will have more capabilities and cost more, but it will have
considerably more chances of success. Without this first mission, we
might fall down in basic areas and lose important concepts. This is a
staged, building-block process such as is done in any good scientific
environment."

Davis
is now working with the XSS-11 mission team to make his group's data
useful to the next-generation vehicle launch scheduled for late 2004.
The XSS-11 mission will involve navigating larger distances and
performing more extreme maneuvers.

Meanwhile,
the XSS-10 is in "de-orbit" mode, and it will eventually fall into the
Earth's atmosphere and burn up. In the process, researchers can track
its movement for up to 20 years, though they add that it poses no
danger to other space objects.